Implantable microphones for use with cochlear implants and other hearing systems typically require an implantable converter for receiving the sound reaching the ear of the patient and converting the sound into electrical signals for further processing in the hearing system. Different solutions have been proposed in the past. In one approach, the sound waves reaching the ear are directly converted into electrical signals which can be accomplished in different ways as described, for example, in U.S. Pat. Nos. 3,882,285, 4,988,333, 5,411,467, and WO 96/21333 and EP 0 831 673. However, with this approach, the natural ability of the outer ear of directionally filtering the received sound is lost and/or the attachment of the required converter components can cause adverse reactions of the affected and surrounding tissue.
In another approach, the natural sound receiving mechanisms of the human outer and middle ear are used for converting the received sound into oscillations of the middle ear components (eardrum and ear ossicle), which are subsequently converted into electrical signals. Different converter principles have been proposed. For example, U.S. Pat. No. 3,870,832 describes implantable converters based on electromagnetic principles. However, the relatively high power consumption of such electromagnetic and electrodynamic converters limits their practical application for cochlear implants and other implantable hearing systems.
This disadvantage is obviated by converters based on piezoelectric principles. EP 0 263 254 describes an implantable converter made of a piezoelectric film, a piezoelectric crystal or a piezoelectric acceleration sensor, whereby one end of the converter is cemented in the bone while the other end is fixedly connected with an oscillating member of the middle ear. The problem with this approach is that inflexible connections to the ear ossicles can cause bone erosion, so that cementing converter components in the middle ear space is approached cautiously for mechanical and toxicological reasons. Moreover, the patent reference does not indicate how the body fluids can be permanently prevented from making contact with the piezoelectric materials. Accordingly, there is a risk of biocompatibility problems, so that the piezoelectric properties can deteriorate due to physical and chemical interactions between the piezoelectric material and the body fluids.
U.S. Pat. No. 3,712,962 describes an implantable converter that uses a piezoelectric cylinder or a piezoelectric beam as a converter component that is anchored in the ear in a manner that is not described in detail. This reference, like the aforementioned patent EP 0 263 254, does not describe in detail how body fluids can be permanently prevented from making contact with the piezoelectric materials.
WO 99/08480 describes an implantable converter based on piezoelectric principles, which is attached solely to an oscillating middle ear component, with the counter support being provided by an inertial mass connected with the converter. However, the attachment of the converter to an oscillating middle ear component, such as the ear drum or the ear ossicles, is either not permanently stable or can erode the bone. This risk is aggravated because the mass of the implantable converter is greater than that of passive middle ear implants.
WO 94/17645 describes an implantable converter based on capacitive or piezoelectric principles, that can be fabricated by micromechanical techniques. This converter is intended to operate a pressure detector in the incudo-stapedial joint. Since the stapes in conjunction with the coupled inner ear forms a resonant system, it may not have sufficient sensitivity across the entire range of useful frequencies. This problem applies also to the implantable converters described in WO 97/18689 and DE 100 30 372 that operate by way of hydro-acoustic signal transmission.
U.S. Pat. No. 3,712,962 describes an implantable converter that uses a piezoelectric converter element that is housed in a hermetically sealed hollow body. The implantable converter is held in position by a support element affixed in the bone channel of the stapes tendon or extended from a screw connection with an ossicle of the middle ear space.
WO 97/11575 describes an implantable hearing aid having a piezo-based microactuator. It includes a disk-shaped transducer which is attached to an end of a tube. The tube is adapted to be screwed into a fenestration formed through the promontory.
U.S. Pat. No. 5,842,967 teaches an implantable contactless stimulation and sensing system utilizing a series of implantable magnets.
Summary of Embodiments
In accordance with one embodiment of the invention, an implantable microphone for use in hearing systems includes a housing having a back wall. The back wall has a recess configured to be coupled to an auditory ossicle. The implantable microphone also includes a membrane coupled to a top portion of the housing and a vibration sensor adjacent to the membrane. The membrane is configured to move, e.g., membrane movement may include flexural movement, in response to movement from the auditory ossicle and the vibration sensor is configured to measure the movement of the membrane and to convert the measurement into an electrical signal. The sensor element can be regarded as a force measurement cell inserted into the ossicle chain.
In accordance with related embodiments, the vibration sensor may be a piezoelectric sensor and the piezoelectric sensor may be shaped as a rectangular bar. The piezoelectric sensor includes piezoelectric material. Movement of the piezoelectric sensor causes deformation of the piezoelectric material and evokes voltage and charge transfer on at least two electrodes of the piezoelectric sensor, thus providing a voltage or charge measurement signal. The housing may have a sidewall between the top portion and the back wall and the vibration sensor may be a) coupled to the sidewall and/or b) in contact with the membrane to move in response to the membrane movement. The implantable microphone may further include one or more additional vibration sensors adjacent to the vibration sensor. The one or more additional vibration sensors may be coupled to the sidewall. The implantable microphone may further include one or more spring elements coupled to the vibration sensor and/or the one or more additional vibration sensors. The spring elements may be configured to contact the housing. The spring elements assist in keeping the one or more vibration sensors in contact with each other and the membrane so that the movement of the vibration sensor(s) correlates to the membrane motion. Membrane motion may include flexural motion which may entail bending, compression and/or shear deformation of the membrane. The implantable microphone may further include an element positioned between the vibration sensor and the membrane. The element may be configured to move the vibration sensor in response to movement from the membrane. The recess may include a channel extending to at least one sidewall of the housing. The recess in the back wall may be substantially aligned with a center of the membrane. The vibration sensor may include a stack of vibration sensors. The vibration sensor may be coupled to the membrane. The membrane may further include a structure substantially positioned at the center of the membrane.
In accordance with another embodiment of the invention, an implantable microphone configured to be coupled to an auditory ossicle includes a housing having a top portion, a back wall, and a sidewall between the top portion and the back wall. The implantable microphone also includes a membrane coupled to the top portion of the housing and a vibration sensor coupled to the sidewall and adjacent to the membrane. The membrane is configured to move in response to movement from the auditory ossicle and the vibration sensor is configured to measure the movement of the membrane and convert the measurement into an electrical signal.
In accordance with another embodiment of the invention, an implantable microphone for use in hearing systems includes a housing having a back wall, a first membrane coupled to a top portion of the housing, and a second membrane coupled to the back wall of the housing. The first and second membranes are configured to move in response to movement from an adjacent auditory ossicle. The microphone also includes a vibration sensor in contact with the first and second membranes. The vibration sensor is configured to measure the movement of the first and second membranes.
In accordance with another embodiment of the invention, an implantable microphone may be designed without a rigid housing, but instead has flexible membranes that act as the housing which are encapsulated by a single or multilayer coating film. Accordingly, an implantable microphone for use in hearing systems includes a vibration sensor and a flexible housing surrounding the vibration sensor. The housing includes a first membrane and a second membrane and both membranes are configured to move in response to movement from an adjacent auditory ossicles. The first membrane and/or the second membrane is in contact with the vibration sensor. The implantable microphone may further include one or more additional vibration sensors adjacent to the vibration sensor. The flexible housing may surround the vibration sensor and the one or more additional vibration sensors and the first membrane and/or the second membrane may be in contact with the vibration sensor and/or one or more of the additional vibration sensors. The vibration sensor and the one or more additional vibration sensors may be separated by a space. The space may include a material that is electrically insulating and that is an elastic, viscous, and/or viscoelastic material. The implantable microphone may further include one or more clamping elements electrically connecting one portion of the vibration sensor to one portion of the one or more additional vibration sensors. The membranes may be encapsulated by an hermetic, elastic, bio resistant and/or bio compatible coating film or films. The vibration sensor may include one or more sensor elements formed by one or more vibration sensor elements or by a stack of vibration sensor elements. The sensing elements, in combination with the encapsulation, may be mechanically designed in such a way as to have approximately the same mechanical characteristics (e.g., elasticity) as that of the cartilage of a joint in the ossicle chain, e.g., the incudo stapedial joint.